Synchronization with an arbitrary phase shift in a pair of synaptically coupled neural oscillators

The phase dynamics of a pair of spiking neural oscillators coupled by a unidirectional nonlinear connection has been studied. The synchronization effect with the controlled relative phase of spikes has been obtained for various coupling strengths and depolarization parameters. It has been found that the phase value is determined by the difference between the depolarization levels of neurons and is independent of the synaptic coupling strength. The synchronization mechanism has been studied by means of the construction and analysis of one-dimensional phase maps. The phase locking effect for spikes has been interpreted in application to the synaptic plasticity in neurobiology.     

Mechanism of the phase transformation of the pyrochlore phase into the perovskite phase in lead zirconate titanate films on silicon substrates

The phase transformation from the pyrochlore phase into the perovskite phase in ferroelectric films of lead zirconate titanate on silicon substrates due to annealing of samples has been investigated experimentally and theoretically. It has been proved that this transformation is a typical first-order phase transition, which is accompanied by a change in the density of the phases and the release of the latent heat of the phase transition. The quantitative evaluations have demonstrated that the difference in the densities of two phases, namely, the perovskite phase and the original parent pyrochlore phase, leads to the generation of elastic stresses in the original parent phase. In turn, these stresses bring about the nucleation of micropores in the bulk of the lead zirconate titanate film. The thermodynamic conditions providing the formation of micropores have been established and the critical size of the micropores has been calculated. A characteristic relationship between the critical size of nuclei of the perovskite phase and the radius of micropores at which the perovskite phase is separated from the parent pyrochlore phase has been derived. This relationship has been verified experimentally. The sizes of the micropores have been determined using scanning electron microscopy, and the changes in the phase composition during the phase transformation have been found using an electron probe X-ray microanalysis. It has been demonstrated theoretically and experimentally that the relaxation of elastic stresses in the lead zirconate titanate thin films during the phase transition occurs through the nucleation and growth of micropores at the interface between the new and parent phases.     

The phase transition in annealed mechanically alloyed Fe - Cu

Using M?ssbauer spectra and x-ray diffraction patterns, annealed mechanically alloyed Fe - Cu has been investigated in this paper. It is found that in [Formula: see text], after it has been milled, fcc-Cu has transformed into bcc-Cu, and some Cu atoms have diffused into the Fe. After the alloy has subsequently been annealed, it is found that bcc-Cu has transformed back into fcc-Cu, while the Cu atoms in the Fe have been separated. In [Formula: see text], after being milled, an fcc-Fe-rich phase has been formed, and after the alloy has subsequently been annealed, this has transformed back to bcc-Fe. The shorter the milling time and the higher the annealing temperature, the faster the transformation. In [Formula: see text], after it has been annealed, the fcc-Fe-rich phase has transformed to bcc-Fe also, and the fcc-Cu-rich phase remains when the annealing temperature increases. All of these results show that the fcc-Fe-rich phase in the milled samples is a metastable phase - it will transform to stable bcc-Fe when it is annealed - while the long-milling-product fcc-Cu-rich phase is a stable phase.     

单模光纤中四波混频的自诱导相位匹配

报道了无双折射单模光纤中四波混频的一种新型相位匹配方式,这种相位匹配仅由抽运光产生的自相位调制和互相位调制的共同作用即可提供,文中报道了实验结果,并从理论上成功地解释了该四波混频相位匹配的机理,与实验符合得很好。     

On the type of a phase transition in the system of exciton polaritons in an optical microcavity

The type of a phase transition in the quasi-equilibrium system of exciton polaritons in a two-dimensional optical microcavity has been analyzed. It has been shown that, although the system contains two types of bosons undergoing mutual transformations into each other, only one phase transition to the superfluid state with the quasilong-range order occurs in the two-dimensional system. This phase transition is a Kosterlitz-Thouless phase transition. A new physical implementation—excitons in a photon crystal—has been proposed for the Bose condensation of exciton polaritons. The superfluid properties of the ordered phase are discussed, and the superfluid density and Kosterlitz-Thouless transition temperature have been calculated in the low-density approximation.     

Spontaneous Breaking of Translational Invariance and Spatial Condensation in Stationary States on a Ring. I. The Neutral System

We consider a model in which positive and negative particles with equal densities diffuse in an asymmetric, CP-invariant way on a ring. The positive particles hop clockwise, the negative counterclockwise, and oppositely charged adjacent particles may swap positions. The model depends on two parameters. Analytic calculations using quadratic algebras, inhomogeneous solutions of the mean-field equations, and Monte Carlo simulations suggest that the model has three phases: (1) a pure phase in which one has three pinned blocks of only positive or negative particles and vacancies and in which translational invariance is broken; (2) a mixed phase in which the current has a linear dependence on one parameter, but is independent of the other one and of the density of the charged particles; in this phase one has a bump and a fluid, the bump (condensate) containing positive and negative particles only, the fluid containing charged particles and vacancies uniformly distributed; and (3) the mixed phase is separated from the disordered phase by a second-order phase transition which has many properties of the Bose–Einstein phase transition observed in equilibrium. Various critical exponents are found.     

交错跃迁Hofstadter梯子的量子流相

为玻色Hofstadter梯子模型引入交错跃迁,来扩展模型支持的量子流相.基于精确对角化和密度矩阵重整化群计算发现,无相互作用时,系统中包含横流相、涡旋相和纵流相;横流相来自均匀跃迁时Hofstadter梯子模型的Meissner相,纵流相是交错跃迁时才可见的流相.强相互作用极限下系统的超流区也包含横流相、纵流相和涡旋相,但存在更多的相变级数;超流区的横流相、纵流相之间存在相变但Mott区的不存在,把Mott区的"横、纵流相"称为Mott-均匀相,在Mott区只存在均匀相和涡旋相.跃迁的交错会压缩涡旋相存在的区域,使Mott区最终只剩下均匀相;跃迁的交错不仅能驱动Mott-超流相变,还使磁通的改变也能够驱动系统的Mott-超流相变.对这一系统的研究丰富了磁通系统中的量子流相,同时为研究拓扑流特性提供了模型支持.     

First-order phase transition through an intermediate state

The theory of first-order phase transitions in systems where the direct formation of nuclei of a new phase is inhibited for any reason, for example, because of the extremely high elastic energy, has been constructed using the example of the silicon-silicon carbide phase transition due to the chemical reaction with carbon monoxide. It has been shown that, in this case, the phase transition occurs through an intermediate state, which significantly promotes the formation of new-phase nuclei. For the silicon-silicon carbide phase transition, such an intermediate state is the “pre-carbide” state of silicon saturated with dilatation dipoles, i.e., pairs formed by a carbon atom and a silicon vacancy that are strongly attracted to each other. The model dependence of the potential energy of systems with an intermediate phase on the reaction coordinates has been investigated. The kinetics of transformation of the intermediate state into a new phase has been described.     

Phase transitions in barium–strontium titanate films on MgO substrates with various orientations

A comparative study of the lattice dynamic upon phase transitions in a polycrystalline Ba_0.8Sr_0.2TiO₃ (BST) film on a Pt substrate and in epitaxial BST films grown on various sections of an MgO substrate has been performed by Raman spectroscopy. It has been found that different sequences of phase transitions take place in these films. The BST/Pt films demonstrate the same sequence of phase transitions that is observed in the bulk ceramics. The hardening of a soft mode in BST/(001)MgO and BST/Pt films shows that the transition from the tetragonal ferroelectric phase to the paraelectric phase has features of the displacement-type phase transition and also the order–disorder phase transition. When approaching the ferroelectric transition temperature, the soft mode in the BST/(111)MgO film is softened, following the Cockran law, which indicates the displacement-type phase transition.     

High-frequency phase recovery of distorted wavefront and analysis on phase correction effect

By constructing a distorted wavefront with random phase screen, the correction process of distorted wavefront has been simulated, and the correction effect of deformable mirror has been simulated and analyzed with the method of high-pass filtering. The variations of correction effect and high-frequency phase distortion have been quantitatively analyzed. The results show that the beam quality of the corrected beam degrades obviously with the increase of high-frequency phase. In addition, a new method has been presented to recover the high-frequency phase of distorted wavefront according to the given intensity distribution and low-frequency phase in near field and the intensity distribution in far field. It shows that the method is very effective to recover the high-frequency phase of distorted wavefront.     

Special phase mask and related data format for page-based holographic data storage systems

Random phase masks in object and reference beam of page-based holographic storage systems suppress the DC-peak and improve the overlap of both beams inside the storage material. Furthermore, they allow for a narrow shift-selectivity. In a holographic setup the phase mask has to be introduced at a conjugate image plane of the spatial light modulator (SLM), if it is not fixed directly on the SLM itself. A binary phase mask with cells generating 0 and π phase shifts has to be aligned very accurately with respect to the SLM pixels, otherwise image artifacts disturb the received data page. We present a phase mask, where the phase cells have the size of a data block which consists of a rectangular set of SLM pixels. Additionally, the corresponding data page has no data at the position of phase jumps and thus relaxes the alignment tolerance significantly.     

基于双频投影条纹的全自动相位解包裹方法

为了在相位轮廓测量术中更简便可靠地获取待测面的相位场,提出了一种利用双频投影条纹的叠栅特性进行全自动相位解包裹的方法。该方法通过分析双频投影条纹的条纹级数之间及相位之间的关系,推导了一套利用该双频条纹的相位主值获取真实相位场的公式。在利用这套公式进行解包裹时,各点的相位求取都是单独进行的,因此不会出现误差传递的现象;同时求解的相位场保持了相移法求解的相位精度。实验证实了该方法的可行性,并得到很好的测量结果。     

Secure optical system that uses fully phase-based encryption and lithium niobate crystal as phase contrast filter for decryption

In this paper, the implementation of a secure optical system using fully phase encryption is described. A two-dimensional phase image obtained from an amplitude image is encrypted and decrypted by using a spatial light modulator working in phase mode. The fully phase encryption is achieved using double random phase encoding. The encrypted image is holographically recorded in a photorefractive crystal and is then decrypted by generating, through phase conjugation, the conjugate of the encrypted image. A lithium niobate crystal has been used as a phase contrast filter to change the decrypted phase image into an amplitude image, thus alleviating the need for alignment of the phase contrast set-up in the Fourier plane. Simulation results are provided to verify the proposed study. The mean square error between the primary image and decrypted image has been calculated to study the sensitivity of the system.     

Competing orders in FeAs layers

Using the unrestricted Hartree-Fock approximation and Landau theory we identify possible phases competing with superconductivity in FeAs layers. We find that close to half-filling the transition from the paramagnet to the magnetically ordered phase is first order, making anharmonicities relevant and leading to a rich phase diagram. Between the already known one-dimensionally modulated magnetic stripe phase and the paramagnet we find a new phase which has the same structure factor as the former but in which magnetic moments at nearest-neighbor sites are at right angles making electrons acquire a nontrivial phase when circulating a plaquette at strong coupling. Another competing phase has magnetic and charge order and may be stabilized by charged impurities.     

Experimental Observation of the Ground-State Geometric Phase of Three-Spin XY Model

The geometric phase has become a fundamental concept in many fields of physics since it was revealed.Recently,the study of the geometric phase has attracted considerable attention in the context of quantum phase transition,where the ground state properties of the system experience a dramatic change induced by a variation of an external parameter.In this work,we experimentally measure the ground-state geometric phase of the threespin XY model by utilizing the nuclear magnetic resonance technique.The experimental results indicate that the geometric phase could be used as a fingerprint of the ground-state quantum phase transition of many-body systems.     

Phase‐Dependent Quantum Correlation in a Cavity‐Atom System

A scheme to manipulate quantum correlation between output lights of a cavity‐atom system by phase control is proposed. A driving‐field phase is introduced which has a similar value with that of building up quantum correlation in a Hanbury–Brown–Twiss setup. A closed‐loop phase is formed to improve quantum coherence by phase‐dependent electromagnetically induced transparency. The closed‐loop phase has been utilized to realize quantum correlation and even quantum entanglement in the atomic system of previous work. With these two phases, a steady and maximum quantum correlation has been obtained in the scheme here. Moreover, the maximum quantum correlation is free to decoherence of this cavity‐atom system. The study on field‐intensity correlation (quantum correlation) has potential applications on correlated imaging, image encryption transmission, and the improvement of noise resistance in a quantum network.     

移相干涉术的一种新算法：重叠四步平均法

提出了一种能大大地减小由于移相器的位移误差而引起相位复原误差的新方法，即重叠四步平均法（Ｏｖｅｒｌａｐｐｉｎｇ Ａｖｅｒａｇｉｎｇ ４－Ｆｒａｍｅ （ＯＡＦ） Ａｌｇｏｒｉｔｈｍ）。给出了这种方法的盯们复原精度与移相器的位移误差之间的关系式，从关系式中可见，ＯＡＦ算法大大地减小由于移相器的位移误差而引起相位复原误差，通过计算机模拟，得到了各种算法的相位复原精度与移相器的位移误差之间的关系曲线，分析     

Evidence of the hexagonal columnar liquid-crystal phase of hard colloidal platelets by high-resolution SAXS

A vast majority of compounds with bent core or banana shaped molecules exhibit the phase sequence B₆-B₁-B₂ as the chain length is increased in a homologous series. The B₆ phase has an intercalated fluid lamellar structure with a layer spacing of half the molecular length. The B₁ phase has a two dimensionally periodic rectangular columnar structure. The B₂ phase has a monolayer fluid lamellar structure with molecules tilted with respect to the layer normal. Neglecting the tilt order of the molecules in the B₂ phase, we have developed a frustrated packing model to describe this phase sequence qualitatively. The model has some analogy with that of the frustrated smectics exhibited by highly polar rod like molecules.     

Image encryption using fractional Mellin transform,structured phase filters,and phase retrieval

An image encryption scheme has been presented by using two structured phase masks in the fractional Mellin transform (FrMT) plane of a system, employing a phase retrieval technique. Since FrMT is a non-linear integral transform, its use enhances the system security. We also add further security features by carrying out spatial filtering in the frequency domain by using a combination of two phase masks: a toroidal zone plate (TZP) and a radial Hilbert mask (RHM). These masks together increase the key space making the system more secure. The phase key used in decryption has been obtained by applying an iterative phase retrieval algorithm based on the fractional Fourier transform. The algorithm uses amplitude constraints of secret target image and the ciphertext (encrypted image) obtained from multiplication of fractional Mellin transformed arbitrary input image and the two phase masks (TZP and RHM). The proposed encryption scheme has been validated for a few grayscale images, by numerical simulations. The efficacy of the scheme has been evaluated by computing mean-squared-error (MSE) between the secret target image and the decrypted image. The sensitivity analysis of the decryption process to variations in various encryption parameters has also been carried out.